IBM Midrange System DS4000 Series Hardware Manual page 263

The following modification priority rates are available:
Lowest
Low
Medium
High
Highest
Note: The lowest priority rate favors system performance, but the modification operation
takes longer. The highest priority rate favors the modification operation, but system
performance might be compromised.
The progress bar at the bottom of the Logical Drive Properties window displays the
progress of a modification operation.
When a storage system logical drive is a primary logical drive and a full synchronization is
necessary, the controller owner performs the full synchronization in the background while
processing local I/O writes to the primary logical drive and associated remote writes to the
secondary logical drive. The full synchronization diverts controller processing resources from
I/O activity, where it can impact performance on the host application. The synchronization
priority defines how much processing time is allocated for synchronization activities relative to
system performance.
The guidelines in Table 4-10 can help determine how long a synchronization can take and
how much various synchronization priorities can affect system performance.
Table 4-10 Impact of modification priority on relative time for full synchronization
Modification priority
Highest
High
Medium
Low
Lowest
Relative time
Fastest possible time
Two times longer than fastest possible time
Three and a half times longer than fastest possible time
Six times longer than fastest possible time
Eight times longer than fastest possible time
Chapter 4. IBM System Storage DS planning and configuration
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